Knife sharpener



FIG. 1 is a Perspective view of a knife sharpener showing my new design;

FIG. 2 is a Front elevational view thereof;

FIG. 3 is a Rear elevational view thereof;

FIG. 4 is a Left side view thereof;

FIG. 5 is a Right side view thereof;

FIG. 6 is a Top plan view thereof; and,

FIG. 7 is a Bottom plan views thereof. 

CLAIM The ornamental design for a knife sharpener, as shown and described. 